Major donors to each of the three big political parties have been included on a list of 30 new peers appointed to the House of Lords.

The working peers, nominated by the party leaders and cleared by independent House of Lords Appointments Commission, included JCB boss Sir Anthony Bamford, whose family and firm have given £2.5 million to the Conservatives in recent years, Scottish businessman Sir William Haughey, who has given £1.3 million to Labour and Domino's Pizza entrepreneur Rumi Verjee, who has given more than £800,000 to the Liberal Democrats.

Also ennobled are several former MPs, members of the European Parliament and devolved assemblies and party officials, as well as justice campaigner Doreen Lawrence, who becomes a baroness on the Labour benches, journalist Daniel Finkelstein, made a Tory lord, and nightclub developer James Palumbo who is elevated to the peerage for the Liberal Democrats.

The list includes 14 Conservatives, 10 Liberal Democrats and five Labour nominees, as well as the first Green to be appointed a peer - London Assembly member and former deputy mayor Jenny Jones, who was selected for nomination by a ballot of party members.

The appointments restore the Conservatives' position as the largest party in the House of Lords by a single seat, with 222 peers to Labour's 221 and the Liberal Democrats' 99. The total number of members of the Upper House - which has already been criticised for being overcrowded - swells to 785, compared to 650 MPs in the House of Commons and 766 MEPs in the European Parliament.

Peers are not paid a salary, but they are entitled to a £300 tax-free allowance for every day they attend a parliamentary sitting. On the basis of 137 sitting days last year, the 30 new peers would have cost the taxpayer around £1.2 million, plus travel and other expenses.

The extra spending could leave David Cameron facing awkward questions after he repeatedly insisted that the cost of politics should not be allowed to rise. The coalition's plans to cut the number of MPs from 650 to 600 have already been dropped, and the Independent Parliamentary Standards Authority is proposing they should receive a significant pay rise.

A Tory source defended the peerage for Sir Anthony, describing him as a "leading industrialist who has made a "massive contribution to British business". JCB has enjoyed a number of ministerial visits since Mr Cameron became Prime Minister, including the opening of a plant in Brazil by the PM himself. But the Conservative source pointed out that as business secretary, Labour's Lord Mandelson had also taken the JCB boss with him on a trade mission.

Mrs Lawrence's seat in the Upper House as a Labour baroness comes after a 20-year fight for justice for her son Stephen, who was stabbed to death at the age of 18 in a racist attack in south London.

Labour leader Ed Miliband said: "Since the horrific racist murder of her son, Doreen has shown incredible strength and courage as she sought, and continues to seek, justice for Stephen. She has changed attitudes to policing and racism in this country and I have no doubt that her strength and determination will be a huge asset to the House of Lords in the coming years."